The invention is based on a method and an apparatus as generally described. In internal combustion engines, such as Diesel engines, equipped with exhaust gas recirculation systems, it is known to adapt the exhaust gas recirculation rate to prevailing operating conditions, for instance recirculating a greater or lesser proportion of exhaust gas expelled by the Diesel engine depending upon the engine load status. It is thereby possible, for instance, to reduce exhaust gas components which are harmful to health; it is also possible, by regulating the exhaust gas recirculation rate as precisely as possible together with the quantity of fresh air supplied and the quantity of fuel injected, to attain an optimal air excess over the entire operating range of the engine, thereby reducing the oxides of nitrogen and attaining a largely soot-free combustion.
Problems may arise in known exhaust gas recirculation systems of this type if the initial operating conditions change and introduce additional variables into the process, which have to be taken into consideration in establishing the exhaust gas recirculation rate. The nature of such variables is, however, such that over the operating life of the engine their influence on the overall course of combustion and exhaust gas recirculation is extremely strong at first but then drops off gradually.